The present invention relates to a processing technique and, more particularly, to a technique effectively applied to thermal processing in manufacture of semiconductor devices.
In manufacture of semiconductor devices, it is general practice to employ a thermal oxide film forming apparatus wherein a substrate of a semiconductor such as silicon, i.e., a wafer, is oxidized under heating in an oxidizing atmosphere in order to form an oxide film on the wafer.
One type of conventional thermal oxide film forming apparatus has heretofore been arranged such that a reaction tube is horizontally disposed, and a wafer is inserted into the reaction tube from one end thereof and placed in position and then heated at a predetermined temperature by means of a heater provided around the reaction tube, and while doing so, a reaction gas containing a predetermined amount of oxygen is supplied into the reaction tube and held therein for a predetermined period of time, thereby forming an oxide film of a predetermined thickness on the surface of the wafer.
However, the present inventors have found that the apparatus of the type described above suffers from the following disadvantage. Namely, when a wafer is inserted into the reaction tube from one end thereof, the outside air is undesirably induced to enter, together with the wafer, the inside of the reaction tube due to, for example, the difference between the temperature of the outside air and that of the interior of the reaction tube which has already been heated to a predetermined temperature. In consequence, the surface of the wafer is disorderly oxidized by the oxygen contained in the outside air which has undesirably entered the reaction tube, thus causing the quality of the oxide film formed on the wafer to be deteriorated, disadvantageously.
Examples of literature describing the technique for forming an oxide film on a wafer include "Denshi Zairyo (Electronic Material)" (an extra number of 1984), Kogyo Chosakai Publishing Co., Ltd., Nov. 15, 1983, pp. 39 to 44.